Sectional transducer



Sept 22 1964 c. J. L UcY SECTIONAL TRANSDUCER Filed July 1'7, 1959 INVENTOR. (HA/#L65 :Ilz/cr United States Patent C) 3,150,275 SECTIONAL TRANSDUCER Charles J. Lucy, Bradford, Pa., assignor to Corning Glass Works, Corning, N.Y., a corporation of New York Filed July 17, 1959, Ser. No. 827,880 4 Claims. (Cl. S10-9.8)

This invention relates to delay line transducers and more specifically to a sectional transducer exhibiting low terminal capacity and a high radiation resistance.

As will be hereinafter referred to, the word transducer is used to mean a device made of material which, when a pulse of electrical energy is applied thereto is capable of transforming the electrical energy into mechanical energy. Conversely, when mechanical energy is applied thereto, it possesses the ability of being able to transform the mechanical energy into a pulse of electrical energy.

This transducer material can be any one of a number of crystalline substances found in nature or, may be any one of a number of synthetic or artificially produced materials. By way of example, this previously discussed phenomenon, also known as Piezoelectricty is exhibited by naturally occurring materials such as crystals of Rochelle salts, quartz and by certain ceramic or artificially produced materials of the class of titanates, zirconates and metaniobates in combination with various metal earth elements. By way of further example, which should not be construed as limiting my invention, the artificially produced or ceramic transducer group includes the lead, barium, and barium plus calcium titanates; lead zirconate; lead and sodium plus potassium metaniobates.

Before a ceramic transducer will exhibit the piezoelec tric effect it must be polarized or poled in any one of many well-known manners. After being properly poled, the major difference between the two types of transducers resides in the fact that the natural crystals exhibit a somewhat higher radiation resistance than the ceramic transducers exhibit a relatively high and, therefore, awkward terminal capacitance, with consequent low electrical impedance, making them diiiicult to work with when considering the fact that the output impedance of the circuit acting as a driver for the transducer is of a relatively high order ranging from about 1,000 to about 10,000 ohms.

Additionally, the radiation resistance of a ceramic transducer, depending on its active area, operating frequency, thickness, mode of vibration and dielectric constant, will vary from about 3 to 100 ohms. y

The characteristics exhibited by ceramic transducers, namely very high capacity and low radiation resistance, causes considerable coupling circuit difiiculty when trying to obtain optimum power transfer and proper matching. A typical prior art transducer assembly utilizing a nominal l megacycle transducer having electrodes on each of its broad surfaces and one of its electrodes cemented to a delay line usually has a radiation resistance of about 4 ohms and a terminal capacitance of about 6,000 mmfd. With a terminal capacitance of 6,000 mmfd. With a terminal capacitance of 6,000 mmfd. it becomes extremely diflicult to resonate the transducer at a frequency of about l0 rnc. because of the extremely low values of inductance required. At this point it would seem that the most obvious solution would be to lower the driver impedance. However, this is not possible because the transducer is usually driven by a normally high impedance as representated by the anode circuit of an oscillator stage. With these values of impedance it will also be appreciated by those skilled in the art, that the lower impedance as represented by a cathode follower is still of too high an order to eiiiciently match the impedance of the transducer.

It, therefore, becomes apparent that if the radiation ice resistance were raised, and if the terminal capacitance of the transducer were substantially reduced, many benefits may be derived therefrom; namely, the lowered capacitance of the transducer were substantially reduced, many benefits may be derived therefrom; namely, the lowered capacitance would now require higher and more reasonable and workable values of inductance to resonate in the 10 mc. range. Having a better match brings about a better and more eiiicient transfer of energy. Also since the electrical bandwidth of the transducer is effectively limited by the terminal capacitance, lowering the capacitance serves to broaden the electrical bandwidth characteristics for a given value of terminating resistance.

I have found that by providing series transducers in either the input or the output or both input and output circuits of a delay line, I am able to increase the terminal radiation resistance and materially decrease the terminal capacitance to values which will more readily lend themselves to conventional coupling circuit design.

It is, therefore, one object of this invention to provide a delay line transducer having a lower terminal capacitance.

Another object of my invention is to provide a delay line transducer capable of being easily and eiiiciently coupled to conventional coupling circuits.

A further object of my invention is to provide a delay line transducer exhibiting better electrical bandwidth characteristics than heretofore possible.

These objects as well as other advantages and more detailed objects of this invention will become more readily apparent to those skilled in the art when read in conjunction with the following disclosure of the embodiments thereof illustrated by the attached drawings in which:

FIGS. 1, 2 and 3 represent three embodiments respectively of my sectional transducer. In each of these figures, like elements are denoted by common numerals.

In FIG. l, transducers 12a and 12b are shown mounted on delay line 14. While delay line 14 has been indicated as a multiple reiiection delay line, it will be obvious to those skilled in the art that my invention has equal applicability to other ultrasonic delay line configurations. Both transducers 12a and 12b are bonded to delay line 14 by bottom electrodes 16a and 16b respectively. Top electrodes 18a and 18b are applied to the other broad surface of transducers 12a and 12b respectively. Lead 20 represents the connection between the bottom electrode 16a of transducer 12a to the top electrode 18b of transducer 12b. Input lead 22 is applied to top electrode 18a of transducer 12a while lead 24 represents the return lead from bottom electrode 16b of transducer 12b. As indicated, this last mentioned lead may be a ground return. Thus, transducers 12a and 12b are connected in series and, as indicated by the polarity signs associated with the respective transducer, the input is applied through lead 22 to the positively poled side of transducer 12a. Lead 20 connects the negatively poled side of transducer 12a to the positively poled side of transducer 12b, and lead 24 connects the negatively poled side of transducer 12b to the other terminal of the input circuit.

By so connecting transducers 12a and 12b, the transducer capacitance existing between electrodes 18a-16a is now in series with the capacitance that exists between electrodes 18b-16b. Therefore, the total capacitance existing between leads 22-24 may be expressed by the formula Where: CT=Total capacitance mmfd.

Ca=Transducer 12a capacitance mmfd. Cb=Transducer 12b capacitance mmfd.

Since the capacitance of each transducer is approximately equal we may then write the Equation 1 as:

mit (2) CT-2CD- 2 Where:

Thus, where for example the capacitance of a typical transducer, according to the prior art, may be of the order of 6,000 mmfd., by utilizing the principles of my invention, the total terminal capacitance has been reduced to a capacitance of the order of 3,000 mmfd. and now represents only 50.0% of its former capacitance.

Since the radiation resistance of each transducer is now in series, the total radiation resistance has, therefore, effectively been doubled.

Referring now to FIGURE'Z, there is shown an embodiment wherein a single transducer 12 is bonded to delay line 14 by bottom electrodes 16a and 16b. Here too, lead 20 connects bottom electrode 16a to top electrode 18b while leads 22 and 24 are connected to top electrode 18a and bottom electrode 16b respectively. Here too, the transducer operates in a manner similar to the transducers 12a and 12b of FIGURE 1,

Referring now to FIGURE 3, there is shown still another embodiment now using a common bottom electrode 16 which bonds transducerslZa and 12b to delay line 14. However, in this embodiment, lead 22 is connected to top electrode 18a of transducer 12a while lead 24 is connected to the top electrode 18b of transducer 12b. It should be noted that in this embodiment the polarity of transducer 12b must be reversed from that shown in the prior embodiments.

By arranging the electrodes and transducers in the manners described, I have also greatly facilitated the manufacture of my sectional transducers.

In FIG. 1, a single transducer can be bonded to a delay line by a single bottom electrode. Then, the top electrode may be applied. Thereafter, it becomes a simple matter to apply a saw or other cutting device to the transducer to accomplish the separation therein indicated. Then, all that remains to be done is to attach leads 20, 22, and 24 to accomplish the series connections.

Regarding the ease of manufacture of FIG. 2, it will be seen by those skilled in the art that a bottom electrode may be rst applied to the delay line and then cut by some saw means to provide the separation. Thereafter, the single transducer 12 may be applied and bonded to the two bottom electrodes. Suitable top electrodes are then applied. Similarly, leads20, 22 and 24 are then attached to provide the series combination.

In FIG. 3, the bottom electrode 16 is first applied toy the delay line and if desired, a single unpoled transducer ,4 may then be bonded thereto. A top electrode is then applied to the transducer which may now be cut by some saw means and thereafter poled to provide the polarity indicated.

As an alternate to the embodiment of FIG. 3, it is suggested that after the bottom electrode is applied, previously poled transducers may be bonded thereto While observing the indicated polarity. Thereafter, top electrodes 18a and 18b and leads 22 and 24 respectively mayy be connected` thereto to provide the necessary input connections.

While I have described what is presently considered a preferred embodiment of my invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the inventive concept contained therein, and it is, therefore, aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of my invention.

What is claimed is:

1. A method of producing an improved ultrasonic delay line ycomprising the steps of: forming one electrode on a delay line facet, bonding electromechanical transducing material to said electrode, applying another electrode to said transducing material and cutting through both said electrodes and said transducing material to form two separate transducers.`

2. The method of claim 1 further including the steps of providing a pair of input terminals and connectingy y said input terminals and said transducers in series.

3. The method` of producing an improved ultrasonic delayline comprising the steps of: forming a bottom electrode on a yfacet of said delay line, bonding oppositely poled surfaces of a pair of electromechanical transducers to said electrode and applying a pair of top electrodes to each of said transducing elements.

4. The method of claim 3 further including the steps of providing a pair of input terminals and respectively connecting each said input terminal to corresponding ones of said top electrodes to connect said transducing elements in series.

References Cited in the le of this patent UNITED STATES PATENTS 

1. A METHOD OF PRODUCING AN IMPROVED ULTRASONIC DELAY LINE COMPRISING THE STEPS OF: FROMING ONE ELECTRODE ON A DELAY LINE FACET, BONDING ELECTROMECHANICAL TRANSDUCING MATERIAL TO SAID ELECTRODE, APPLYING ANOTHER ELECTRODE TO SAID TRANSDUCING MATERIAL AND CUTTING THROUGH BOTH SAID ELECTRODES AND SAID TRANSDUCING MATERIAL TO FORM TWO SEPARATE TRANSDUCERS. 